An alphanumeric password is a secret made from letters and numbers, and sometimes symbols, instead of digits alone. Compared with a short numeric PIN, it usually has far more possible combinations, which makes guessing and brute-force attacks harder.
In cyber security, alphanumeric passwords are often used for account recovery or two-step verification because they raise the cost of automated attacks and simple social engineering. They are still only as strong as their length, randomness, and secrecy: predictable words, reused passwords, or patterns like names and dates can be cracked much faster. Defenders prefer longer, unique alphanumeric passwords because they are easier to store and enter than cryptographic keys, while still providing a stronger barrier than a basic PIN.